Light emitting diode (LED) driving circuit

Abstract

A light emitting diode (LED) driving circuit is provided. The LED driving circuit includes a voltage adjusting unit, a switch unit, and a control unit. The control unit is coupled to the voltage adjusting unit and the switch unit. The voltage adjusting unit outputs a driving voltage to a first end of each of a plurality of load units. The switch unit is coupled to a second end of each of the load units. When one LED string in the load units is coupled to a current source, the voltage adjusting unit adjusts the voltage level of the driving voltage so that the voltage level of the driving voltage of the driving voltage corresponds to the driven LED string. Thereby, a driving problem caused by the variation in electrical characteristics of the LEDs is alleviated.

What is claimed is: 
     
       1. A light emitting diode (LED) driving circuit, for driving a plurality of load units, each of the load units including at least an LED, the LED driving circuit comprises:
 a voltage adjusting unit, for outputting a driving voltage to a first end of each of the load units; 
 a switch unit, coupled between a current source and a second end of each of the load units, the switch unit selectively coupling one of the load units to the current source; and 
 a control unit, coupled to the voltage adjusting unit and the switch unit, the voltage adjusting unit adjusting the driving voltage according to a first control signal generated by the control unit, the switch unit selectively coupling the one of the load units to the current source according to a second control signal generated by the control unit; 
 wherein when the switch unit couples a first load unit of the load units to the current source, the voltage adjusting unit adjusts a voltage level of the driving voltage so that the voltage level of the driving voltage corresponds to the first load unit. 
 
     
     
       2. The LED driving circuit of  claim 1 , wherein when the switch unit couples a second load unit of the load units to the current source, the voltage adjusting unit adjusts the voltage level of the driving voltage so that the voltage level of the driving voltage corresponds to the second load unit. 
     
     
       3. The LED driving circuit of  claim 1 , wherein when the switch unit sequentially couples a series of load units to the current source, the voltage adjusting unit adjusts the voltage level of the driving voltage so that the voltage level of the driving voltage sequentially corresponds to the series of load units or one of the coupled load units. 
     
     
       4. The LED driving circuit of  claim 1 , wherein the switch unit comprises:
 a plurality of switches, coupled between the current source and the load units, respectively; and 
 a switch control unit, coupled to the switches, for selectively turning on the switches according to the second control signal. 
 
     
     
       5. The LED driving circuit of  claim 4 , wherein the switches comprise N-type transistors or P-type transistors. 
     
     
       6. The LED driving circuit of  claim 1 , wherein the voltage adjusting unit comprises a boost circuit or a buck circuit. 
     
     
       7. The LED driving circuit of  claim 1 , wherein the load units at least comprise an LED string, the LED string comprises a plurality of serially connected first LEDs. 
     
     
       8. The LED driving circuit of  claim 1 , wherein the current source is a constant current source.